This invention relates to a resolver system for detecting the angular position and rotational speed of a rotating element.
Amongst conventional resolvers, a bipolar variable reluctance type resolver is known, e.g. from Japanese Provisional Patent Publication (Kokai) No. 1-218344, which comprises a rotor and a stator which are arranged such that the reluctance of a space between the rotor and pole shoes formed on the stator varies with a change in the angular position of the rotor in such a fashion that one revolution of the rotor causes one cycle of a fundamental wave of reluctance variation, wherein the reluctance variation is sensed to detect the angular position and/or rotational speed of the rotor, the stator having formed thereon three first pole shoes circumferentially arranged at intervals of 120.degree., the first pole shoes having wound thereon three-phase AC excitation windings and output windings, and three second pole shoes circumferentially arranged at locations diametrically opposite to respective ones of the first pole shoes, the second pole shoes having wound thereon three-phase AC excitation windings and output windings which have a reverse winding direction to that of the output windings on the first pole shoes, the six first and second pole shoes being generically called "the group A", the stator further having six pole shoes generically called "the group B" circumferentially arranged at locations deviated by 90.degree. from respective ones of the pole shoes of the group A, the pole shoes of the group B having wound thereon AC excitation windings and output windings in an identical arrangement with the group A. The phase difference (.theta.+.pi./4) between an output voltage, which is obtained by synthesizing output voltages from the output windings of the groups A, B, and an excitation voltage applied to each of the excitation windings is detected, to detect the angular position .theta. of the rotor with reference to a reference position of -.pi./4.
However, according to the known resolver, each of the pole shoes formed on the stator is surrounded by both an excitation winding for forming a magnetic field and an output winding for detecting an output signal which has been phase-modulated by an amount corresponding to the rotational angle of the rotor. Therefore, a large space is required for accommodating the windings, resulting in an increased size of the whole resolver. Furthermore, the excitation winding and the output winding on each pole shoe has to be electrically insulated from each other, which requires an increased number of manufacturing steps as well as a complicated winding operation, leading to an increased manufacturing cost.